1. Field of the Invention
The present invention relates to a polarizer. This invention also relates to a polarizing plate and an optical film using the polarizer concerned. Furthermore, this invention relates to an image display, such as a liquid crystal display, an organic electroluminescence display, a CRT and a PDP using the polarizing plate and the optical film concerned.
2. Description of the Prior Art
Liquid crystal display are rapidly developing in market, such as in clocks and watches, cellular phones, PDAs, notebook-sized personal computers, and monitor for personal computers, DVD players, TVs, etc. In the liquid crystal display, visualization is realized based on a variation of polarization state by switching of a liquid crystal, where polarizers are used based on a display principle thereof. Particularly, usage for TV etc. increasingly requires display with high luminance and high contrast, polarizers having higher brightness (high transmittance) and higher contrast (high polarization degree) are being developed and introduced.
As polarizers, for example, since it has a high transmittance and a high polarization degree, polyvinyl alcohols having a structure in which iodine is absorbed and then stretched, that is, iodine based polarizers are widely used (for example, Japanese Patent Laid-Open No. 2001-296427). However, since the iodine based polarizers have relatively low polarization degrees in short wavelength side, they have problems in hue, such as blue omission in black display, and yellowing in white display, in short wavelength side.
Iodine based polarizers may easily give unevenness in a process of iodine absorption. Accordingly, there has been a problem that the unevenness is detected as unevenness in transmittance particularly in the case of black display, causing to decrease of visibility. For example, as methods for solving the problems, several methods have been proposed that an amount of absorption of iodine absorbed to the iodine based polarizer is increased and thereby a transmittance in the case of black display is set not higher than sensing limitations of human eyes, and that stretching processes generating little unevenness itself are adopted. However, the former method has a problem that it decreases a transmittance in the case of white display, while decreasing a transmittance of black display, and as a result darkens the display itself. And also, the latter method has a problem that it requires replacing a process itself, worsening productivity.